Extensible dust-collecting shroud for grinders

ABSTRACT

A rotary abrading tool has a dust removal accessory that accommodates for wearing of the abrading member. The tool has a portable housing having a handgrip portion and a rotatably driven shaft extending from the housing. A backing plate is mounted to an end of the shaft for rotation therewith, An abrading member mounted to the backing plate. A shroud base is stationarily mounted to the housing around the backing plate. A plurality of concentric rings of successively smaller diameters are carried by the base, each of the rings having an outer diameter that frictionally engages an inner diameter of another one of the rings. The rings are movable relative to the base from a contracted position to an extended position, defining a generally conical enclosure that surrounds the abrading member. An exhaust tube extending from the base for creating a suction within the base and the conical enclosure to collect dust particles.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of provisional application No. 60/334,467, filed Nov. 30, 2001.

FIELD OF THE INVENTION

[0002] This invention deals with dust collecting shrouds for rotary abrasive tools such as grinders.

BACKGROUND OF THE INVENTION

[0003] The dust created by abrasive tools as they abrade a workpiece can be hazardous to the workers health. While masks are commonly worn, it is also desirable to prevent as much dust as possible from dispersing into the air around the worker. Dust collecting shrouds are employed around the tool. Typically, the shroud is connected through a vacuum tube to a vacuum source. The shroud is secured by a bracket to the tool and is of a fixed length that extends to the abrading member.

[0004] Shrouds of this nature work well enough for grinders employing sand paper. When the sand paper is worn sufficiently for replacement, the shroud distal end will still be approximately aligned with the sand paper because the difference in thickness between new sand paper and worn sand paper is small. Other types of abrading members, however, are much thicker when new than when worn. One type comprises a disk with a plurality of resilient fingers or bristles extending from the disk. The bristles are used to remove paint, particularly in marine applications. The bristles wear down with use. Abrasive stones also wear in thickness. Hole cutters of a type using a circular sawtooth band don't wear in thickness, however, the distance between the workpiece and the tool decreases as the hole is being cut. In all of these instances a rigidly mounted shroud of fixed length will not accommodate the decreasing distance from the tool to the workpiece.

SUMMARY

[0005] A rotary abrading tool accessory attaches to a rotary abrading tool having a shaft that rotates a backing plate that has an abrading member attached thereto. The accessory has a shroud base that fits around the backing plate. A telescoping enclosure section extends from the base for enclosing the abrading member. The telescoping enclosure section has a length that is axially variable. An exhaust tube extends from the base for creating a suction within the enclosure section and the base to collect dust particles.

[0006] In the preferred embodiment, the telescoping section is made up of a plurality of concentric rings that overlap and frictionally engage each other to create an enclosure. The rings are of successively smaller diameters in a direction away from the base. Preferably, the rings are formed by coiling a resilient metal band, with each turn of the coil creating another ring.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:

[0008]FIG. 1 is a perspective view of a portable abrasive grinder of the invention showing the shroud surrounding the backing plate and abrasive disk with portions of the shroud broken away for ease of illustration;

[0009]FIG. 2 is a sectional view of the shroud, backing plate and abrasive disk used with the grinder of FIG. 1; and

[0010]FIG. 3 is a plan view of the bottom surface of the abrasive disk.

DETAILED DESCRIPTION OF THE INVENTION

[0011]FIG. 1 shows a portable abrading tool, which is an abrasive grinder 11. Grinder 11 has a handgrip 12 and a control valve 13. Control valve 13 is coupled to a remote air source through a conduit 15 in order to power a motor 17 having a vertically oriented output shaft 19. Grinder 11 can be, for instance, a DOTCO Sander Model No. 10L1280-36, right angle, air powered, rear exhaust, 12,000 rpm, 3 inch sanding disk capacity, available from DCM Clean-Air Products, Inc., Fort Worth, Tex. Grinders of the type under consideration typically operate at speeds on the order of 12,000-20,000 rpm for driving a 3 inch disk.

[0012] Referring to FIG. 2, output shaft 19 of motor 17 is joined by a coupling 21 to a backing plate 23 for driving the backing plate 23 in rotary fashion about the vertical axis defined by the output shaft 19. Grinder 11 may be used to drive any rotary implements adapted for use on high-speed grinders.

[0013] Backing plate 23 has an upper surface 25, a lower surface 27 and a plurality of holes 29 which communicate the upper and lower surfaces 25, 27. As shown also in FIG. 3, lower surface 27 of the backing plate 23 has a circular periphery, and a plurality of holes 29 are circumferentially spaced a radial distance from the vertical axis at regular angular intervals. Lower surface 27 has an internal threaded female connector 31 that is coaxial with the vertical axis and used for securing an abrasive member 33 to the plate. Backing plate 23 may be formed of any appropriate material which is sufficiently resilient to press abrasive member 33 against a work surface 35 and return backing plate 23 to an approximately planar condition when abrasive member 33 is out of contact with work surface 35. For instance, backing plate 23 can be formed of an appropriate fabric-reinforced resinous plastic material, such as a suitable phenolic. Alternatively, backing plate 23 could be made of a hard rubber.

[0014] An extensible shroud 37 encircles backing plate 23 and is connected by means of a conduit 39 to a commercially-available vacuum source (not shown) for removing dust particles from work surface 35. The term “dust particles” means spent abrasive particles and other particulate matter created by the abrading operation and which are entrained in the air flowing through shroud 37 and through conduit 39 to the dust collection point. Shroud 37 is designed to be used with any type of rotary grinding or cutting implement that is attached to output shaft 19 and fits within shroud 37.

[0015] Referring to FIG. 2, shroud 37 has a shroud base 38 that is a cylindrical member with a closed proximal end, the proximal end being the closer end to handgrip 12. The distal end of shroud base 38 is open. Shroud base 38 is retained in position by securing it to a support arm 43 (FIG. 1) having an appropriate opening to receive output shaft 19 of the motor 17.

[0016] Shroud 37 also has a telescoping enclosure section comprising a thin band 40 of resilient metal wound in a plurality of turns to create a helix. The helix is coaxial with the output shaft 19, and each 360 degree turn decreases in diameter by the horizontal thickness of the band, creating a plurality of rings 41 of progressively smaller diameter. Each ring of band 40 overlaps bears frictionally against another of the rings. The largest diameter ring 41 has one end attached to shroud base 38, and the smallest diameter ring has the opposite end of band 40 attached within. Rings 41 of shroud 37 can translate in a direction parallel to the axis of output shaft 19 and can tilt slightly relative to the axis of output shaft 19. Grasping the smallest diameter ring 41 and pulling it away from shroud base 38 causes rings 41 to move to an extended position, defining a conical enclosure. An outward facing lip 45 is preferably formed on the proximal edge of band 40. An inward facing lip 47 is preferably formed on the distal edge of band 40. Lips 45, will engage each other when in the fully extended position to retain rings 41 in the coiled configuration. Each lip 45, 47 engages a surface of an adjacent ring 41, providing a substantially air tight seal for the telescoping enclosure defined by rings 41.

[0017] The inner surface of the innermost and most distal ring 41 has a radius approximately ¼″ larger than that of the backing plate 23. The space permits the intake of dust particles from work surface 35 about the periphery of the backing plate 23. Preferably, shroud 37 has an extended length that is selected so that the distal end of band 40 is approximately flush with the distal end of an unworn abrasive member 33. Rings 41 allow the length of shroud 37 to decrease as it is pushed against the work surface 35.

[0018] Alternatively, though not shown in the figures, shroud 37 may be formed from a plurality of nested cones. The cones are coaxial with output shaft 19, each having a slightly larger upper diameter than lower diameter. The diameter of each subsequent inner cone decreases by the horizontal thickness of the cones, and the cones frictionally engage each other. The outer cone is secured to the support arm 43, but the inner cones can translate in a direction parallel to the axis of the output shaft 19. The inner cones move independently of and relative to each other. Any two adjacent cones can move relative to each other any distance less than the vertical height of the cones.

[0019]FIGS. 2 and 3 show one type of abrasive member 33 that secures to backing plate 23. Abrasive member 33 is circular in shape and has a bottom surface 51, a top surface or disk 53 and a plurality of circumferentially-spaced holes 55. The number of holes 55 is equal to the number of holes 29 in backing plate 23 to permit alignment of the holes 29, 55. Top surface 53 of member 33 has a threaded male connector 57 for securing member 33 to backing plate 23.

[0020] Member 33 has a plurality of resilient bristles or fingers 59 depending from the bottom surface 51 and extending parallel to the vertical axis. A clearance between rings 41 and fingers 59 allows fingers 59 to flare outwardly without contacting the inner surface of the innermost ring 41. The lower ends of fingers 59 are applied to work surface 35 while member 33 is rotating to remove material from work surface 35. As the work surface 35 abrasion process continues, the ends of fingers 59 are also abraded, and the lengths of fingers 59 decrease. Extensible shroud 37 accounts for this decrease in length by allowing inner bands 41 to move axially relative to each other to decrease the extended length of shroud 37.

[0021] The proper use of the grinder 11 is shown in FIG. 2. Grinder 11 is held at a 3-5 degree angle relative to work surface 35, and the rear portion of the lower edge of the innermost turn or ring 41 is placed against work surface 35. Fingers 59 near the rear of shroud 37 contact work surface 35, but the front edge of innermost ring 41 and fingers at the front are held above work surface 35. As fingers 59 rotate and brush against work surface 35, fingers 59 remove particles from work surface 35. The tips of fingers 59 are also abraded during this process, and this decreases the lengths of the fingers 59. To account for this decrease, the grinder assembly is moved toward the work surface 35 while maintaining the 3-5 degree tool angle, and the innermost ring 41 moves toward the support arm 43 until fingers 59 contact the work surface 35.

[0022] The invention has significant advantages. The shroud provides efficient dust collection for abrading tools that cause the tool to become nearer to the workpiece during use. The shroud is particularly useful for abrasive members that wear significantly in thickness.

[0023] Although the invention has been described with respect to a threaded connector between the backing plate 23 and abrasive member 33, other arrangements could be used as well, as long as the particular engagement means provides for the male connector 57 to fit loosely in a first rotary position and to be turned through a predetermined degree of rotation to a second binding position, the degree of rotation being calculated to cause alignment of the member holes 55 with the holes 29 of the backing plate 23.

[0024] While the invention has been shown in only one of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit thereof. 

1. A rotary abrading tool accessory for attachment to a rotary abrading tool having a shaft that rotates a backing plate that has an abrading member attached thereto, the accessory comprising: a shroud base adapted to fit around the backing plate, the base having an axis that is adapted to coincide with an axis of the shaft; a telescoping enclosure section extending from the base for enclosing the abrading member, the telescoping enclosure section having a length that is axially variable; and an exhaust tube extending from the base for creating a suction within the enclosure section and the base to collect dust particles.
 2. The abrading tool accessory according to claim 1, wherein the base has an enclosed proximal end into which the exhaust tube extends.
 3. The abrading tool accessory according to claim 1, wherein the telescoping section comprises a plurality of rings of successively smaller diameters.
 4. The abrading tool accessory according to claim 1, wherein the telescoping section comprises a band that is helically wound in a plurality of rings, with each successive ring being farther from the base and of a smaller diameter.
 5. The abrading tool accessory according to claim 1, wherein the telescoping section comprises a resilient metal band that is helically wound in a plurality of rings, with each successive ring exerting a radially outward directed frictional force against a preceding ring.
 6. The abrading tool accessory according to claim 1, wherein the telescoping section comprises a resilient metal band having an outward protruding lip at a proximal edge of the band and an inward protruding lip at a distal edge of the band, the band being helically wound to define a plurality of rings, with the lips of each successive ring engaging each other as the telescoping section is moved to the fully extended position.
 7. The abrading tool accessory according to claim 1, further comprising a bracket for mounting the base stationarily to the abrading tool.
 8. A rotary abrading tool, comprising: a portable housing having a handgrip portion; a rotatably driven shaft extending from the housing; a backing plate mount to an end of the shaft for rotation therewith; an abrading member mounted to the backing plate; a shroud base stationarily mounted to the housing around the backing plate; a plurality of concentric rings of successively smaller diameters carried by the base, each of the rings having an outer diameter that frictionally engages an inner diameter of another one of the rings, the rings being movable relative to the base from a contracted position to an extended position, defining a generally conical enclosure that surrounds the abrading member; and an exhaust tube extending from the base for creating a suction within the base and the conical enclosure to collect dust particles.
 9. The rotary abrading tool according to claim 8, wherein the rings comprise flat metallic bands.
 10. The rotary abrading tool according to claim 8, wherein the rings are formed from a single, resilient metallic band that is wrapped helically in a plurality of turns, with each of the turns defining one of the rings.
 11. The rotary abrading tool according to claim 8, wherein the rings are formed from a single, resilient metallic band that is wrapped helically in a plurality of turns, with each of the turns defining one of the rings, the band having an outward protruding lip on a proximal edge and an inward protruding lip on a distal edge, the lips engaging each other when the band is in the extended position.
 12. The rotary abrading tool according to claim 8, wherein the abrading member comprises: a disk secured to the backing plate; a plurality of resilient fingers extending from the disk for abrading a workpiece; and a plurality of holes extending through the disk that register with holes provided in the backing plate.
 13. The rotary abrading tool according to claim 8, further comprising a bracket connecting the shroud base to the housing.
 14. A rotary abrading tool accessory for attachment to a rotary abrading tool having a shaft that rotates a backing plate that has an abrading member attached thereto, the accessory comprising: a shroud base adapted to fit around the backing plate, the base having an axis that is adapted to coincide with an axis of the shaft; a flat, resilient metallic band having one end attached to the shroud base and coiled in a plurality of turns that overlap and frictionally engage one another to define a telescoping enclosure of variable length for extending around the abrading member; and an exhaust tube extending from the base for creating a suction within the enclosure section and the base to collect dust particles.
 15. The abrading tool accessory according to claim 14, wherein the band has an outward protruding lip on a proximal edge and an inward protruding lip on a distal edge, the lips engaging each other when the band is in an extended position.
 16. A method for abrading a workpiece, comprising: mounting an abrading member to a backing plate, the backing plate being attached to a shaft of a rotary abrading tool; mounting a shroud around the backing plate, the shroud having a telescoping section that encloses the abrading member; connecting an exhaust tube to the shroud; gripping the rotary abrading tool, rotating the shaft, placing the abrading member and the telescoping section against a workpiece and creating a suction within the shroud to collect dust particles created by the abrading member; and as the abrading member wears, causing the telescoping section to reduce in length. 